Acid-catalyzed dehydration of naphthalene-cis-1,2-dihydrodiols: Origin of impaired resonance effect of 3-substituents

Article abstract of DOI:10.1021/jo201591r

Acid-catalyzed dehydrations of substituted naphthalene-cis-1,2-dihydrodiols occur with loss of the 1- or 2-OH group to form 2- and 1-naphthols, respectively. Effects of substituents MeO, Me, H, F, Br, I, and CN at 3-, 6-, and 7-positions of the naphthalene ring are consistent with rate-determining formation of β-hydroxynaphthalenium ion (carbocation) intermediates. For reaction of the 1-hydroxyl group the 3-substituents are correlated by the Yukawa-Tsuno relationship with ρ = -4.7 and r = 0.25 or by σ_p constants with ρ = -4.25; for reaction of the 2-hydroxyl group the 3-substituents are correlated by σ_m constants with ρ = -8.1. The correlations for the 1-hydroxyl imply a surprisingly weak resonance interaction of +M substituents (MeO, Me) with a carbocation reaction center but are consistent with the corresponding correlation for acid-catalyzed dehydration of 3-substituted benzene-cis-1,2-dihydrodiols for which ρ = -6.9 and r = 0.43. Substituents at the 6- and 7-positions of the naphthalene rings by contrast are correlated by σ⁺ with ρ = -3.2 for reaction of the 1-hydroxyl group and ρ = -2.7 for reaction of the 2-hydroxyl group. The unimpaired resonance implied by these substituent effects appears to be inconsistent with a previous explanation of the weak resonance of the 3-substituents in terms of imbalance of charge development and/or nonplanarity of the benzenium ring in the transition state. An alternative possibility is that the adjacent hydroxyl group interferes sterically with conjugation of +M substituents. "Hyperaromaticity" of the arenium ion intermediates does not appear to be a factor influencing this behavior.

Full text of DOI:10.1021/jo201591r

Article
pubs.acs.org/joc
Acid-Catalyzed Dehydration of Naphthalene-cis-1,2-dihydrodiols:
Origin of Impaired Resonance Effect of 3-Substituents
Jaya Satyanarayana Kudavalli,† Derek R. Boyd,‡ Narain D. Sharma,‡ and Rory A. More O’Ferrall*,†
†School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
‡School of Chemistry and Chemical Engineering, The Queens University of Belfast, Belfast BT9 5AG, Northern Ireland
S
* Supporting Information
ABSTRACT: Acid-catalyzed dehydrations of substituted naphthalene-cis-1,2-
dihydrodiols occur with loss of the 1- or 2-OH group to form 2- and 1-naphthols,
respectively. Effects of substituents MeO, Me, H, F, Br, I, and CN at 3-, 6-, and 7-
positions of the naphthalene ring are consistent with rate-determining formation
of β-hydroxynaphthalenium ion (carbocation) intermediates. For reaction of the
1-hydroxyl group the 3-substituents are correlated by the Yukawa−Tsuno
relationship with ρ = −4.7 and r = 0.25 or by σp constants with ρ = −4.25; for reaction of the 2-hydroxyl group the 3-substituents
are correlated by σm constants with ρ = −8.1. The correlations for the 1-hydroxyl imply a surprisingly weak resonance interaction
of +M substituents (MeO, Me) with a carbocation reaction center but are consistent with the corresponding correlation for acid-
catalyzed dehydration of 3-substituted benzene-cis-1,2-dihydrodiols for which ρ = −6.9 and r = 0.43. Substituents at the 6- and
7-positions of the naphthalene rings by contrast are correlated by σ+ with ρ = −3.2 for reaction of the 1-hydroxyl group and
ρ = −2.7 for reaction of the 2-hydroxyl group. The unimpaired resonance implied by these substituent effects appears to be
inconsistent with a previous explanation of the weak resonance of the 3-substituents in terms of imbalance of charge
development and/or nonplanarity of the benzenium ring in the transition state. An alternative possibility is that the adjacent
hydroxyl group interferes sterically with conjugation of +M substituents. “Hyperaromaticity” of the arenium ion intermediates
does not appear to be a factor influencing this behavior.
Scheme 2
INTRODUCTION
■
There is considerable evidence that arene 1,2-dihydrodiols,
such as benzene dihydrodiol (1), undergo acid-catalyzed
dehydration to give the corresponding phenol by the
mechanism shown in Scheme 1, for which the rate-determining
Scheme 1
reported to yield a ρ value of −7.0, which is of a magnitude
expected of a carbocation reaction, but a value of r, which is a
sensitive indicator of resonance, with the surprisingly low value
of 0.3. This implied that resonance effects of MeO, EtO, and
alkyl substituents (e.g.) are not much greater than their effects
on the ionization of benzoic acids, with r = 0.27.4 Indeed, a
reasonable correlation was obtained when logs of rate constants
were plotted against σp, the substituent constant based on the
ionization of (p-substituted) benzoic acids.2
step is formation of a β-hydroxy carbocation intermediate.1,2
The carbocation may lose a proton or undergo a hydride ion
rearrangement (NIH shift) as alternative pathways to product
formation.3 However, the product forming steps do not
influence the effect of substituents on the rate of reaction.
The influence of 3-substituents on dehydration of benzene-
cis-1,2-dihydrodiols 3, in which the 1-OH acts as a leaving
group (Scheme 2), was described some years ago.2 Surprisingly,
despite the formation of a carbocation intermediate 4 in which
the substituent is directly conjugated with the positive charge,
the reaction is quite insensitive to +M resonance effects. Thus,
application of the Yukawa−Tsuno relationship (eq 1) was
(1)
It is perhaps worth remarking that the substituent X in
structures 3 and 4 formally occupies a “meta” position with
respect to the site of reaction and at first sight might not have
been expected to be in conjugation with it. However, we may
recognize that carbocation 4 corresponds to the Wheland
intermediate of an electrophilic hydroxylation reaction in which
Received: July 30, 2011
Published: October 12, 2011
© 2011 American Chemical Society
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the X-substituted benzene is attacked by OH+. The structure of
4 implies that attack of the electrophile has occurred ortho to X
and that conjugation of X with the positive charge is indeed
expected.
6-methyl-, 7-cyano-, and 7-methoxy-substituted metabolites the
yields obtained were too small for kinetic studies.
The anomalous resonance behavior for the dehydration of
benzene-cis-1,2-dihydrodiols is of interest partly because it has
been proposed that the carbocation intermediate 4 is unusual in
possessing aromatic character1 as a consequence of hyper-
conjugation between the methylene group and π-delocalized
positive charge within arenium ions.5 This character is most
simply expressed in terms of valence bond resonance structures
illustrated for the benzenium ion (5a ↔ 5b) in which the no-
bond structure associated with hyperconjugation is subject to
exceptional stabilization arising from its aromatic character.
Experimental evidence for this behavior has been summarized
in a number of papers and includes the very large difference in
reactivity between isomeric cis- and trans-benzene-1,2-dihy-
drodiols, kcis/ktrans = 4500.1,6,7 This difference can be under-
stood in terms of formation of carbocation intermediates in
which the C−H and C−OH bonds respectively at the 2-
position are oriented in pseudoaxial positions favorable for
hyperconjugation and the much greater (“positive”) hyper-
conjugative ability of the C−H than the C−OH bond.
First-order rate constants kobs for dehydration were measured
spectrophotometrically in aqueous HClO4 at 25 °C. Second-
order rate constants were obtained from the slopes of linear
plots of the first-order constants against acid concentration or,
for slower reactions for which the use of concentrated acid was
necessary, from the intercepts of plots of log(kobs/[H+]) against
the acidity parameter X0.10 Because, normally, both 1- and 2-
naphthols were found as products, the rate constants were
partitioned on the basis of product fractions for the two
reaction paths as shown in Scheme 3, in which k1 and k2
Scheme 3
The question thus arises: is the anomalous lack of resonance
contribution in the dehydration of 3-substituted benzene-cis-
1,2-dihydrodiols a reflection of the unusual “hyperaromatic”
character of the carbocation intermediate? To help answer this
question, we describe here the acid-catalyzed dehydration of
naphthalene-cis-1,2-dihydrodiols substituted at the 3-, 6-, and 7-
positions shown arrowed in 6.8
represent rate constants for reaction of the 1- and 2-hydroxyl
groups, respectively, and correspond to rate-determining
formation of 1- and 2-(β-hydroxy)naphthalenium ion inter-
mediates (cf. Scheme 1). The measured rate constant
corresponds to k1 + k2 and the ratio of product fractions ([2-
naphthol]/[1-naphthol]) to k1/k2. The product fractions were
determined by HPLC or proton NMR analysis. They are
shown together with the conditions of measurement in the
Supporting Information (Table S1). Measured first-order rate
constants are shown in Table S2. The factored second-order
rate constants (k1 and k2) are listed in Table 1.
Analysis of the kinetic data is based chiefly on application of
the Yukawa−Tsuno relationship.4,11 This makes use of
substituent constants σ+ and σ0, convenient compilations of
which have been provided by Exner,12 Leffler and Grunwald,13
and Tsuno and Fujio.14
Insofar as reactions of OH leaving groups at both the 1- and
2-positions of the naphthalene ring of structure 6 may be
monitored, the reactions yield a considerable amount of
additional information on substituent effects for the dehy-
dration reactions of dihydrodiols. As shown below, the 3-
substituted naphthalene dihydrodiols follow a similar pattern to
those of the benzene-1,2-dihydrodiols, with a notably restricted
resonance contribution, whereas the 6- and 7-substituents show
the full degree of resonance expected of direct conjugation with
a carbocationic charge.
DISCUSSION
■
The first question that may be asked is: do substituents at the
3-position of the naphthalene-cis-1,2-dihydrodiols 9 experience
the same impairment of resonance interactions with the
developing positive charge in the transition state for the acid-
catalyzed dehydration reaction (Schemes 3 and 4) as
3-substituents in benzene-cis-1,2-dihydrodiols 3?
RESULTS
■
The naphthalene-cis-1,2-dihydrodiols used in this study were
obtained as products of bacterial oxidation of the corresponding
2-substituted naphthalene substrates by dioxygenase enzymes
present in cultures of Pseudomonas putida UV4. The structure
and absolute stereochemistry of the isolated metabolites 7−9
have been described earlier.9 The compounds were generally
obtained as mixtures of 3-, 6-, and 7-substituted regioisomers
which were separated by chromatography and characterized by
NMR and other spectroscopic methods. In the case of the
In Scheme 4, reaction of the C-1 hydroxyl group is shown.
This is favored by the resonance interaction with a +M
3-substituent and the less unfavorable inductive effect from a −I
substituent than for reaction of the C-2 hydroxyl group
adjacent to the substituent. In the case of the benzene-cis-1,2-
dihydrodiols 3 reaction occurs very predominantly at the C-1
position, and rate constants for reaction at the 2-position were
deemed too unreliable to justify application of Yukawa−Tsuno
free energy relationship.2
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Table 1. Second-Order Rate Constants (L mol−1 s−1) for Acid-Catalyzed Dehydrations of 3-, 6-, and 7-Substituted Naphthalene-
cis-1,2-dihydrodiols for Loss of 1- and 2-Hydroxyl Groups (k1 and k2, Respectively) in Aqueous HClO4 at 25 °C
3-X
6-X
7-X
X
k1
k2
k1
k2
k1
k2
H
7.00 × 10−5
7.35 × 10−4
1.81 × 10−3
7.20 × 10−6
3.57 × 10−6
4.78 × 10−6
6.9 × 10−8
1.41 × 10−3
1.36 × 10−3
5.6 × 10−5
1.27 × 10−7
8.94 × 10−7
2.05 × 10−6
4.6 × 10−8
7.00 × 10−5
1.41 × 10−3
7.00 × 10−5
9.2 × 10−4
1.41 × 10−3
7.47 × 10−3
Me
OMe
F
0.113
2.32 × 10−3
7.0 × 10−5
1.35 × 10−4
1.44 × 10−4
1.80 × 10−5
2.10 × 10−4
2.85 × 10−5
3.6 × 10−5
2.0 × 10−6
1.59 × 10−5
3.88 × 10−5
1.57 × 10−3
3.62 × 10−4
3.5 × 10−4
Br
I
CN
redetermination based on 11 substituents. Despite its larger
value, it still implies that resonance interaction of 3-substituents
is impaired for these acid-catalyzed dehydration reactions
compared with a “normal” carbocation reaction. This
conclusion is endorsed by the even smaller value of 0.25 for
the 3-substituted naphthalene-cis-1,2-dihydrodiols. By compar-
ison, for the solvolysis of cumyl chlorides, the defining reaction
for σ+, ρ = −4.84 and by definition r = 1.0.
Scheme 4
In the case of the naphthalene dihydrodiols, however, the
substituent preference for reaction at the C-1 position is
compensated by an intrinsically greater reactivity of the C-2
than C-1 hydroxyl group. For the unsubstituted naphthalene
dihydrodiol 6, the C-2 hydroxyl group is more reactive by a
factor of 20. For other X substituents ratios of reactivity range
from this value to 32 in the opposite direction for a 3-methoxy
group which strongly activates reaction of the 1-hydroxyl, as
expected of the resonance interaction illustrated in Scheme 4.
Thus, substituent effects can be determined with similar
precision for reactions of both hydroxyl groups.
Considering first the reaction of the C-1 hydroxyl group,
which may be directly compared with the corresponding
reaction of the benzene-dihydrodiols, application of the
Yukawa−Tsuno relationship to rate constants for the 3-
substituted naphthalene-cis-1,2-dihydrodiols gives values of ρ
= −4.7 and r = 0.25 (Figure 1). These values may be compared
It is possible that the smaller resonance interaction for the
naphthalene dihydrodiols reflects a longer path between
substituent and reaction site and sacrifice of the resonance
stabilization of a benzene ring (Scheme 4, structures 10) when
compared with the carbocations formed from benzene
dihydrodiols. This may also be reflected in the further
reduction in the effect of +M substituents implied by the
smaller ρ value. It is perhaps surprising at first that the ρ value is
smaller, insofar as this is based on inductive effects and that the
distance between the substituent and the reaction site is the
same for benzene and naphthalene dihydrodiols. The difference
presumably arises as a result of a reduction in effective charge
sensed by a −I substituent because of partial delocalization into
the second benzene ring. However, a caveat for over-
interpreting magnitudes of these ρ and r values is noted below.
The most important conclusion from these measurements is
that 3-substituents in the naphthalene-cis-1,2-dihydrodiols are
experiencing similar or indeed greater impairment of resonance
interactions than that observed for the benzene-cis-1,2-
dihydrodiols. This is confirmed by (a) the good linear
correlation with slope 0.745 when logs of rate constants for
3-substituted naphthalene dihydrodiols are plotted against
corresponding values for 3-substituted benzene dihydrodiols
as shown in Figure 2 and (b) by a satisfactory correlation (with
ρ = −4.25) when logs of rate constants for 3-substituted
naphthalene dihydrodiols are plotted agains σp constants based
on the ionization of p-substituted benzoic acids, for which the
resonance contribution is small.
Not much is added to the comparison by consideration of
the effects of 3-substituents upon reaction of the C-2 hydroxyl
group of the naphthalene-cis-1,2-dihydrodiols. Now resonance
between the substituent and site for carbocation formation is
precluded. Altough formally there appears to be an o-
relationsip between the substituent and reaction site, it can
be seen that if the intermediate was generated by electrophilic
attack of OH+ at the 1-position of a 3-substituted naphthalene,
the substituent would be m- to the point of attack.
Correspondingly, the logs of the measured rate constants
show a good correlation with substituent constants σm based
on the ionization of m-substituted benzoic acids (Figure S1).
Significantly ρ = −8.0 is larger than for reaction of the 1-hydroxyl
Figure 1. Yukawa−Tsuno plot for the acid-catalyzed dehydration of 3-
substituted naphthalene-cis-1,2-dihydrodiols 9 in aqueous solution at
25 °C; log k = −4.20 − 4.67{σ0 + 0.25(σ+ − σ0)}, Rsqr = 0.977.
with ρ = −6.9 and r = 0.43 for dehydration of the benzene
dihydrodiols.2 The value of r for the benzene dihydrodiols
differs from that previously reported (0.3)2 and represents a
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Figure 3. Plot of log k for the acid-catalyzed dehydration of 6- and 7-
substituted naphthalene-cis-1,2-dihydrodiols (7, 8) in aqueous
perchloric acid at 25 °C with loss of the 1-hydroxyl group versus
σp+ for 7- and σ+m for 6-substituents; log k = −3.24 − 3.70σ+, Rsqr =
0.934.
Figure 2. Plot of log k for dehydration of 3-substituted naphthalene-
cis-1,2-dihydrodiols with loss of OH at the 1-position against log k for
3-substituted benzene-cis-1,2-dihydrodiols; from measurements in
aqueous HClO4 at 25 °C; slope = 0.745, intercept = −3.38, Rsqr =
0.984.
However, the main inference to be drawn from these results
is the contrast between the strong resonance interactions of +M
substituents at the 6- and 7-positions of the naphthalene ring
and the weaker resonance from the 3-position.
group, consistent with the closer proximity of substituent and
reacting group in this case.
Turning to the 6- and 7-substituted naphthalene-cis-1,2-
dihydrodiols, the obvious question arises, are resonance effects
of these substituents similarly impaired to those of the
3-substituents? The answer is clearly negative. For these
substituents, again we consider reactions of the 1- and 2-
hydroxyl groups independently. However, for both leaving
groups, 6- and 7-substituents may be combined within a
Yukawa−Tsuno correlation. For reaction of the 1-hydroxyl +M
substituents at the 6-position but not at the 7-position are
capable of a resonance interaction with the reaction center, and
vice versa for reaction of the 2-hydroxyl group.
The “normal” values of ρ and degree of resonance for the 6-
and 7-positions strongly suggest that these are not substantially
modified by “hyperaromatic” stabilization of the β-hydroxy
arenium ion intermediate or transition state leading to it. In an
earlier paper it was suggested that the impaired resonance of 3-
substituents in the dehydration of benzene cis-1,2-dihydrodiols
was the result of an imbalance between inductive and resonance
effects at the transition state. This was suggested as arising
because planarity of the five bonds between the electron pair of
a +M substituent and the positive charge at the reaction site
had not been achieved at the transition state with a detrimental
effect on the resonance interaction shown for a methoxy
substituent in structures 11 of Chart 1.
For reaction of the 1-hydroxyl group the importance of
resonance can be seen qualitatively from the reactivity of the
substrate with a 6-methoxy substituent. This is the only
substituent for which the reactivity of the 1-hydroxyl is greater
than the 2-hydroxyl. A Yukawa−Tsuno plot for reaction of the
1-hydroxyl leads to values of ρ = −3.25 and r = 1.0. This
implies that an optimum correlation is achieved for a plot of log
k against σ+ with no contribution from σ0. This plot is shown
Chart 1
+
in Figure 3 with σm values used for substituents at the 7-
position. Both this plot and Figure 1 show a certain amount of
scatter. Probably this reflects the presence of the charge center
in a ring and a somewhat different molecular environment from
the cumyl cation forming reaction for which σ+ is defined.
Limitations of σ + for correlating substituent effects in
electrophilic aromatic substitutions have been discussed by
Taylor.15
For reaction of the 2-hydroxyl group ρ = −2.9, and again
there is a good correlation with σ+ (Figure S2). In this case r is
less well-defined than for reaction of the 1-hydroxyl because
there is no 7-methoxy substituent, and the magnitude of r is
effectively determined by Me and F substituents, for which
resonance contributions to the substituent effects are smaller.
The less negative ρ for reaction of the 2- rather than 1-hydroxyl
group is consistent with the increased number of bonds
between substituent and reaction site.
The resonance interaction of a 3-methoxy substituent with
the reaction site in the dehydration of a naphthalene
dihydrodiol is illustrated by structures 12 of Chart 1. In this
case the distance between substituent and cation center is the
same as for the benzene dihydrodiol, but arguably the fusion of
a benzene ring could increase coplanarity of the π-bonds
involved in the conjugation, favoring a normal resonance
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NMR spectra were run on instruments operating at 300, 400, or 500
MHz. HPLC measurements were made with dual wavelength
absorbance detection. UV−vis spectra and kinetic measurements
were run on a spectrophotometer equipped with an automatic cell
changer which was thermostated at 25 ± 0.1 °C. Column
chromatography was performed on Merck-Kieselgel type 60 9250−
400 mesh silica. Preparative TLC was carried out on glass plates
coated with Merck-KieselgelPF254/366 silica (21 g in 60 mL of water).
Product Analyses. Product analyses were carried out for each of
the 3-, 6-, and 7-substituted naphthalene-cis-1,2-dihydrodiols for which
a rate constant for acid-catalyzed dehydration was determined. These
involved identification of 1- and 2-naphthol products from reaction of
the 2- and 1-hydroxyl groups of the dihydrodiols and determination of
their ratio of concentrations (cf. Scheme 3). As a general procedure,
7−10 mg of reactant in acetonitrile was treated with dilute perchloric
acid for at least seven half-lives of reaction. The reaction mixture was
neutralized with saturated sodium bicarbonate followed by extraction
with ethyl acetate and evaporation of the solvent under reduced
interaction for +M substituents. In practice, the resonance is
even less favorable than for the benzene-cis-1,2-dihydrodiols.
Moreover, if the bonds separating substituent and reaction site
for 3- and 7-substituents are compared (Chart 1, 12 and 13), it
is hard to see why there should not be a similar impairment of
resonance in the case of +M substituents at the 7-position as at
the 3-position.
These considerations suggest that the reduction in resonance
may stem less from the nonplanarity and/or imbalance of
resonance and inductive effects in the transition state than
steric hindrance, preventing the methoxy substituent itself
achieving the planarity necessary for full expression of its
resonance. This is most obviously due to the adjacent hydroxyl
group. It is true that there is little evidence of steric hindrance
to electrophilic aromatic substitution at an ortho position, which
might have been considered a closely related reaction.
However, both reactants and transition states for these
reactions differ, and only the intermediates are strictly
comparable in structure. For the dihydrodiols the steric
influence of the adjacent hydroxyl on conjugation of a
substituent is likely to be enhanced by a buttressing effect
from the reacting hydroxyl group, an effect which is not present
in the transition state for the electrophilic aromatic substitution
reaction.
1
pressure; a H NMR spectrum of the mixture was recorded.
In general, the NMR spectrum revealed two products with two sets
of peaks in the 6.5−8.5 ppm region corresponding to the 1- and 2-
naphthols. The ratio of products was determined from integration of
non-overlapping peaks. The major product was isolated by preparative
TLC, and the structure was assigned by comparison of the spectrum
with an authentic sample or spectrum reported in the literature. The
minor product was presumed to have the complementary structure.
In the case of bromo- and iodonaphthol samples spectra were not
available, and the mixtures of phenolic products were converted to
a mixture of the unsubstituted 1- and 2-naphthols by reductive
hydrogenation. The ratio of naphthol concentrations was determined
by HPLC based on comparison with authentic samples.
The detailed procedure for hydrogenation and analysis of the iodo-
and bromonaphthol products was as follows. The unpurified mixture
of products from the dehydration reaction was dissolved in 5 mL of
methanol and triethylamine (0.05 mL). Pd/C (10 mg) was added
followed by stirring for 10 h under a H2 atmosphere. The solution was
filtered through Celite, and the filtrate was concentrated under
vacuum. The products were analyzed by reverse phase HPLC on a
C18 column with water and acetonitrile as eluants and a flow rate of
1 mL/min.
A caveat for these comparisons is that the precision with which
r values may be determined is quite sensitive to experimental or
“chemical” dispersion within a group of measurements.
Optimization of values involves complementary changes in r
and ρ, so that correlation coefficients are a relatively insensitive
function of one parameter when the other can vary. Chart 2
Chart 2
The spectrophotometric method for kinetic measurements is
outlined in the Results section and Supporting Information and is
described in more detail in previous publications.16 The measured
first-order rate constants are listed in the Supporting Information
(Table S3).
illustrates variation of these parameters between limiting and
optimum combinations of σ0 and σ+ based on 11 substituents
for the previously studied 3-substituted benzene cis-dihydrodiols.
Nevertheless, it is clear that the present results for
naphthalene-cis-1,2-dihydrodiols reinforce the conclusion that
resonance between substituent and reaction site is impaired in
the dehydration of 3-substituted arene-1,2-dihydrodiols. The
proposal that the lack of resonance is mainly steric in origin
remains a tentative one, but it is difficult to envisage an
alternative explanation. Importantly, it seems safe to rule out
any explanation in terms of stabilization of the positive charge
of the intermediate through hyperconjugation enhanced by the
aromatic character of the benzenium (4) or naphthalenium
(10) ion as reactive intermediates. Apart from their chemical
interest, the results are significant in allowing a better
understanding of factors influencing the stabilities under
physiological conditions of an important class of aromatic
metabolites.9
ASSOCIATED CONTENT
■
S
* Supporting Information
Details of product analyses, rate constants, and m* values,
including summary Tables S1−S3: graphical representations of
free energy relationships, Figures S1 and S2. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rmof@ucd.ie.
ACKNOWLEDGMENTS
■
This work was supported by the Science Foundation Ireland
Grant 04/IN3/B581.
EXPERIMENTAL SECTION
■
Instrumentation and Chromatography. All the substituted
naphthalene-cis-1,2-dihydrodiols 3, 6, and 7 were obtained as
enantiopure metabolites of 2-substituted naphthalene substrates
using whole cells of Pseudomonas putida UV4.
REFERENCES
■
(1) Kudavalli, J. S.; Boyd, D. R.; Coyne, D.; Keeffe, J. R.; Lawlor, D.
A.; MacCormac, A. C.; More O’Ferrall, R. A.; Rao, S. N.; Sharma,
N. D. Org. Lett. 2010, 12, 5550−5553.
They were structurally and stereochemically characterized as
described in an earlier paper.8 For the work of the current paper
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